Introduction to multimedia. Analog PowerPoint PPT Presentation

Contents. What is multimedia?Analog representation of audio dataAnalog representation of video dataDigital representation of audio-video dataColor spaces for images. What is multimedia?. media = text, graphics, still images, voice, soundmultimedia = a combination of several media types; ex. aud

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Introduction to multimedia. Analog

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5. Analog signal (audio, video) representation Analog signal - continuous signal for which the time varying feature (variable) of the signal is a representation of some other time varying quantity, i.e., analogous to another time varying signal.
ex.: in sound recording, fluctuations in air pressure representing the actual sound “is analogus” to the variations induced by a vibrating diaphragm in the electrical current/voltage produced by the coil/condensor in an electromagnetic microphone; in radio modulation of a sinusoidal carrier wave (e.g. amplitude modulation – AM, frequency modulation – FM)
advantages:
has the potential of infinite resolution of the signal (high density)
processing is simple
disadvantages:
noise – as the signal is copied and re-copied or transmitted over long distances random variations occur
impossible to recover from noise/distortion

6. Digital signal (audio, video) representation Digital signal = a signal which is represented as a sequence of numbers (usually in binary numbers)
ex.: digital image – matrix of pixels, digital sound – vector of sound amplitudes
advantages:
as opposed to analog signals, degradation of the signal (i.e. noise) can not only be detected but corrected as well
scales well with the increased complexity of the system
disadvantages:
it is error prone (due to quantization and sampling)
it has lower resolution than analog signals

7. Analog-to-digital signal conversion converting a continuous analog signal into a discrete digital signal has 2 subprocesses:
1. sampling - conversion of a continuous-space/time (audio, video) signal into a discrete-space/time (audio, video) signal
2. quantization - converting a continuous-valued (audio, video) signal that has a continuous range (set of values that it can take) of intensities and/or colors into a discrete-valued (audio, video) signal that has a discrete range of intensities and/or colors; this is usually done by rounding, truncation or other irreversible non-linear process of information destruction